The present invention relates to aerosol generators and methods for generating an aerosol. In particular, the aerosol generators are vapor driven, thus are able to generate aerosols without requiring the use of compressed gas propellants. The present invention has particular applicability to the generation of aerosols containing medicated material.
Aerosols are useful in a wide variety of applications. For example, it is often desirable to treat respiratory ailments with, or deliver drugs by means of, aerosol sprays of finely divided particles of liquid and/or solid, e.g., powder, medicaments, etc., which are inhaled into a patient""s lungs. Aerosols are also used for purposes such as providing desired scents to rooms distributing insecticide and delivering paint and lubricant.
Various techniques are known for generating aerosols. For example, U.S. Pat. Nos. 4,811,731 and 4,627,432 disclose devices for administering medicaments to patients in which a capsule is pierced by a pin to release a medicament in powder form. A user then inhales the released medicament through an opening in the device. While such devices may be acceptable for use in delivering medicaments in powder form, they are not suited to delivering medicaments in liquid form. The devices are also, of course, not well-suited to delivery of medicaments to persons who might have difficulty in generating a sufficient flow of air through the device to properly inhale the medicaments, such as asthma sufferers. The devices are also not suited for delivery of materials in applications other than medicament delivery.
Another well-known technique for generating an aerosol involves the use of a manually operated pump which draws liquid from a reservoir and forces it through a small nozzle opening to form a fine spray. A disadvantage of such aerosol generators, at least in medicament delivery applications, is the difficulty of properly synchronizing inhalation with pumping. More importantly, however, because such aerosol generators tend to produce particles of large size, their use as inhalers is compromised because large particles tend to not penetrate deep into the lungs.
One of the more popular techniques for generating an aerosol including liquid or powder particles involves the use of a compressed propellant, often containing a chlorofluoro-carbon (CFC) or methylchloroform, to entrain a material, usually by the Venturi principle. For example, inhalers containing compressed propellants such as compressed gas for entraining a medicament are often operated by depressing a button to release a short charge of the compressed propellant. The propellant entrains the medicament as the propellant flows over a reservoir of the medicament so that the propellant and the medicament can be inhaled by the user.
In propellant-based arrangements, a medicament may not be properly delivered to the patient""s lungs when it is necessary for the user to time the depression of an actuator such as a button with inhalation. Moreover, aerosols generated by propellant-based arrangements may have particles that are too large to insure efficient and consistent deep lung penetration. Although propellant-based aerosol generators have wide application for uses such as antiperspirant and deodorant sprays and spray paint, their use is often limited because of the well-known adverse environmental effects of CFC""s and methylchloroform, which are among the most popular propellants used in aerosol generators of this type.
In drug delivery applications, it is typically desirable to provide an aerosol having average mass median particle diameters of less than 2 microns to facilitate deep lung penetration. Most known aerosol generators are incapable of generating aerosols having average mass median particle diameters less than 2 microns. It is also desirable, in certain drug delivery applications, to deliver medicaments at high flow rates, e.g., above 1 milligram per second. Most known aerosol generators suited for drug delivery are incapable of delivering such high flow rates in the 0.2 to 2.0 micron size range.
U.S. Pat. No. 5,743,251, which is hereby incorporated by reference in its entirety, discloses an aerosol generator, along with certain principles of operation and materials used in an aerosol generator, as well as a method of producing an aerosol. The aerosol generator disclosed according to the ""251 patent is a significant improvement over earlier aerosol generators, such as those used as inhaler devices.
The invention provides methods and apparatus for producing an aerosol by using inductive heating. The inductive heater heats fluid in a fluid passage so as to produce a vapor which forms an aerosol when it is exposed to the air outside the fluid passage.
The inductive heater can include one or more coils that produce an electromagnetic field when an electrical current is passed therethrough. The flux from this electromagnetic field produces eddy currents in a heating element to thereby heat the heating element and transfer heat to the fluid by use of the inductive heater.
The inductive heater can be fabricated using various materials. Preferably, the heating element has electrically conductive material associated with it. For example, the heating element can be made of metal or it can be made of glass and have a metal coating on it. A flux concentrator can optionally be used to increase the flux concentration in the heating element and thereby heat the fluid passage at a faster rate.
In a preferred embodiment, the fluid passage can be in a capillary tube that is replaceable. For example, the tube can be mounted in the aerosol generator such that it can be pulled out and replaced with a new one. In another embodiment, the fluid passage can be a channel in a multilayered composite.